Welding method of low-oxygen monocrystalline silicon seed crystal

Abstract

The invention provides a welding method of a low-oxygen monocrystalline silicon seed crystal, which comprises the following steps: when welding begins, the flow rate of a protective gas is a conventional flow rate, heating is performed until the temperature of a molten silicon liquid level is a first temperature, the flow rate of the protective gas is adjusted to be a first flow rate, and the temperature is continuously increased and the first flow rate is maintained until the seed crystal is welded; the temperature of the molten silicon liquid level is reduced, and the flow of the protective gas is reduced; when the temperature of the molten silicon liquid level is the final temperature, the flow of the protective gas is adjusted to be the final flow; the first temperature is greater than the final temperature, the first flow is greater than the final flow, and the first flow is greater than the conventional flow; and in a fixed period of time, the final flow is kept unchanged, and after the time is over, the flow of the protective gas is recovered to the conventional flow, so that the welding process is completed. According to the invention, the problem of poor crystallization of the low-oxygen single crystal silicon rod caused by high-temperature fusion liquid level shaking is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single crystal silicon, in particular to a low-oxygen single crystal silicon seed melting method. BACKGROUND

[0002] With the continuous upgrading of solar photovoltaic cell manufacturing technology, the quality requirements for single crystal silicon wafers are becoming higher and higher. Among them, the interstitial oxygen content in single crystal silicon wafers exceeding 12ppma will cause the appearance of concentric circles in the battery sheet, affecting the conversion efficiency of solar cells. Therefore, lower oxygen content of single crystal rods has become the direction of single crystal quality efforts.

[0003] In order to achieve this goal, the industry generally adopts low-charge transfer and low-furnace pressure technology. Low-charge transfer can reduce the corrosion of high-purity quartz crucible by molten silicon, thereby reducing the introduction of oxygen atoms, and low-furnace pressure helps to enhance the escape speed of oxygen atoms in the inert gas atmosphere in the single crystal furnace.

[0004] However, in actual production process, the furnace pressure in the single crystal furnace table is too low, and as the temperature in the furnace rises, the molten silicon liquid surface will jump, and the whole crystal melting interface will shake seriously, which will cause the poor quality of the crystal seed and molten silicon melting, and reduce the crystal growth rate. SUMMARY

[0005] To solve the above technical problems, the present application provides a low-oxygen single crystal silicon seed melting method. In view of the molten silicon liquid surface shaking scene during high-temperature melting in the low-charge transfer and low-furnace pressure single crystal rod drawing, it is found that increasing the flow of protective gas during melting can solve the problem of molten silicon liquid surface shaking during high-temperature melting, thereby improving the crystal growth rate.

[0006] To achieve this purpose, the present application adopts the following technical solutions:

[0007] The present application provides a low-oxygen single crystal silicon seed melting method, which comprises:

[0008] At the beginning of melting, the flow of protective gas is the conventional flow. When the temperature of the molten silicon liquid surface is heated to the first temperature, the flow of protective gas is adjusted to the first flow. The temperature is continuously raised and the first flow is maintained until the seed is completed. The temperature of the molten silicon liquid surface is reduced, and the flow of protective gas is reduced. Until the temperature of the molten silicon liquid surface is the final temperature, the flow of protective gas is adjusted to the final flow. The first temperature is greater than the final temperature, the first flow is greater than the final flow, and the first flow is greater than the conventional flow. In a fixed time, the final flow is kept unchanged, and after the time is over, the flow of protective gas is restored to the conventional flow, and the melting process is completed.

[0009] It is worth mentioning that, for the high temperature welding of single crystal rod drawing in low crucible rotation, low furnace pressure, the fluctuation of molten silicon liquid surface is found by trying different solutions, and it is found that increasing the flow of protective gas can well solve the problem of high temperature welding of molten silicon liquid surface. The oxygen content of the low oxygen single crystal silicon is less than or equal to 12ppma, the low rotation of the crucible is less than or equal to 6 revolutions per minute, and the single crystal rod drawing of low furnace pressure is less than or equal to 7 torr.

[0010] But in other running stage of furnace (introducing crystal, shoulder, equal diameter, finishing, etc.), such a large flow of protective gas cannot be used, the reasons are as follows:

[0011] First, increasing the flow of protective gas will inevitably lead to full load operation of the furnace evacuation system, and long time full load operation will greatly increase the failure discipline;

[0012] Second, during the equal diameter process of the furnace, the large flow of protective gas will cause the crystal rod to shake, which is easy to cause production accidents;

[0013] Third, the large flow of protective gas will cause the production cost to rise.

[0014] The welding method of the present application has the following special features, first, in the welding process, the protective gas with a first flow larger than the conventional flow is used for welding, and it is found that the fluctuation of the molten silicon liquid surface can be effectively alleviated, and the crystal yield is significantly improved; second, after the welding is completed, the temperature is reduced while the flow of protective gas is reduced, and the flow of protective gas is gradually reduced under the condition that the molten silicon liquid surface is maintained stable, and the conventional flow of protective gas used in the furnace is restored.

[0015] The welding method in the present application is a step in the crystal pulling process of Czochralski single crystal silicon, which generally includes a melting process, a temperature adjusting process, a welding process, a crystal introducing process, a shoulder releasing process, a shoulder turning process, an early equal diameter process, a middle equal diameter process, a late equal diameter process and a finishing process. The present application only studies the welding process, and the conventional flow refers to the flow of protective gas used in other processes, and the present application generally has no special requirements for the conventional flow, which can be carried out by the flow familiar to those skilled in the art.

[0016] The present application has no special requirements for the melting process, the temperature adjusting process, the crystal introducing process, the shoulder releasing process, the shoulder turning process, the early equal diameter process, the middle equal diameter process, the late equal diameter process and the finishing process in the crystal pulling process of Czochralski single crystal silicon, and the process flow and process parameters familiar to those skilled in the art can be used, and they can also be adjusted according to actual needs.

[0017] Preferably, the regular flow rate is 85-110 slpm, for example, it can be 85 slpm, 86 slpm, 87 slpm, 88 slpm, 89 slpm, 90 slpm, 92 slpm, 95 slpm, 100 slpm, 102 slpm, 105 slpm, 108 slpm or 110 slpm, etc.

[0018] In the present application, slpm refers to the flow rate unit under standard conditions, which is standard liters per minute.

[0019] Preferably, the final temperature of the continuous temperature rise is 1458-1461℃, for example, it can be 1458℃, 1459℃, 1459.5℃, 1460℃, 1460.5℃ or 1461℃, etc.

[0020] Preferably, the first temperature is 1450-1455℃, for example, it can be 1450℃, 1451℃, 1452℃, 1452.5℃, 1453℃, 1453.5℃, 1454℃, 1454.5℃ or 1455℃, etc.

[0021] Preferably, the first flow rate is 25-110 slpm higher than the regular flow rate, for example, it can be 25 slpm, 35 slpm, 37 slpm, 101 slpm or 110 slpm, etc., but is not limited to the listed values, and other unlisted values within the range are also applicable.

[0022] Preferably, the first flow rate is 110-210 slpm, for example, it can be 110 slpm, 120 slpm, 130 slpm, 140 slpm, 150 slpm, 160 slpm, 170 slpm, 180 slpm, 190 slpm, 197 slpm, 199 slpm, 200 slpm, 202 slpm, 204 slpm, 205 slpm, 207 slpm, 209 slpm or 210 slpm, etc., but is not limited to the listed values, and other unlisted values within the range are also applicable.

[0023] Preferably, the first flow rate is 40-60 slpm higher than the regular flow rate, and the first flow rate is controlled within the range of 125-170 slpm, which can significantly improve the crystallization rate.

[0024] Preferably, during the process of reducing the temperature of the molten silicon liquid surface and reducing the flow rate of the protective gas, the relationship between the flow rate Q of the protective gas and the temperature T of the molten silicon liquid surface is Q=aT-b, wherein a ranges from 8.330 to 8.335, for example, can be 8.330, 8.331, 8.332, 8.333, 8.334 or 8.335, etc., and b ranges from 11900 to 12000, for example, can be 11900, 11910, 11920, 11930, 11940, 11950, 11960, 11980, 11990 or 12000, etc. For example, the relationship between the flow rate Q of the protective gas and the temperature T of the molten silicon liquid surface is Q=8.330T-11972, wherein the unit of T is ℃, and the unit of Q is slpm.

[0025] It is further found in the process of gradually reducing the temperature that controlling the relationship between Q and T within the above range can significantly improve the crystal formation rate and avoid the abnormal fusion of the seed crystal caused by the shaking of the molten silicon liquid surface.

[0026] Preferably, during the process of reducing the temperature of the molten silicon liquid surface and reducing the flow rate of the protective gas, the flow rate of the protective gas is adjusted every time the temperature of the molten silicon liquid surface is reduced by 1-5 ℃.

[0027] Preferably, the process of reducing the temperature of the molten silicon liquid surface and reducing the flow rate of the protective gas comprises: reducing the flow rate of the protective gas to A1 flow rate when the temperature of the molten silicon liquid surface is reduced to A temperature in the first reduction; and reducing the flow rate of the protective gas to B1 flow rate when the temperature of the molten silicon liquid surface is reduced to B temperature in the second reduction. Wherein, the A temperature is higher than the B temperature; and the A1 flow rate is greater than the B1 flow rate.

[0028] The application preferably adopts a two-stage adjustment mode of the protective gas flow rate, and the temperature of the molten silicon liquid surface is recognized by the automatic control system of the furnace table and the flow rate of the protective gas is adjusted in real time. The two-stage adjustment mode can facilitate operation while achieving a better crystal formation rate, and has a broad application prospect.

[0029] Preferably, the A temperature ranges from 1455 to 1459 ℃, for example, can be 1455 ℃, 1455.5 ℃, 1456 ℃, 1456.5 ℃, 1457 ℃, 1457.5 ℃, 1458 ℃ or 1459 ℃, etc.; and the A1 flow rate ranges from 150 to 183 slpm, for example, can be 150 slpm, 160 slpm, 165 slpm, 170 slpm, 180 slpm or 183 slpm, etc.

[0030] Preferably, the B temperature ranges from 1450 to 1456°C, for example, it can be 1450°C, 1450.5°C, 1451°C, 1451.5°C, 1452°C, 1452.5°C, 1453°C, 1453.5°C, 1454°C, 1455°C, 1455.5°C, or 1456°C, etc.; the B1 flow rate ranges from 105 to 160 slpm, for example, it can be 105 slpm, 110 slpm, 115 slpm, 120 slpm, 125 slpm, 130 slpm, 135 slpm, 140 slpm, 145 slpm, 150 slpm, 155 slpm, or 160 slpm, etc.

[0031] Preferably, the temperature difference between the A temperature and the B temperature ranges from 3 to 5°C, for example, it can be 3°C, 3.3°C, 3.5°C, 3.7°C, 3.9°C, 4.2°C, 4.4°C, 4.6°C, 4.8°C, or 5°C, etc., but is not limited to the listed values, and other values not listed in this range are also applicable; the flow rate difference between the A1 flow rate and the B1 flow rate ranges from 25 to 35 slpm, for example, it can be 25 slpm, 27 slpm, 28 slpm, 29 slpm, 30 slpm, 31 slpm, 32 slpm, 33 slpm, 34 slpm, or 35 slpm, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0032] When the flow rate of the protective gas is adjusted in two stages, the temperature difference between the A temperature and the B temperature is preferably controlled to be within 3 to 5°C, so that the fluctuation of the molten silicon liquid surface does not affect the crystal quality, and the number of adjustments is reduced, and the flow rate difference between the two stages is controlled to be within 25 to 35 slpm.

[0033] Preferably, the A1 flow rate is lower than the first flow rate.

[0034] Preferably, the difference between the A1 flow rate and the first flow rate ranges from 15 to 25 slpm, for example, it can be 15 slpm, 17 slpm, 18 slpm, 19 slpm, 20 slpm, 21 slpm, 22 slpm, 23 slpm, 24 slpm, or 25 slpm, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0035] Preferably, the final temperature ranges from 1458 to 1461°C.

[0036] Preferably, the terminal flow rate is 120-140 slpm, for example, it can be 120 slpm, 123 slpm, 125 slpm, 127 slpm, 129 slpm, 132 slpm, 134 slpm, 136 slpm, 138 slpm or 140 slpm, etc., but not limited to the listed values, other values not listed in this range are also applicable.

[0037] Preferably, the method further comprises maintaining a certain time within the fluctuation range of the terminal flow rate and within the fluctuation range of the terminal temperature.

[0038] Preferably, the fluctuation range of the terminal flow rate is 0.1-0.5°C fluctuation up and down on the terminal temperature, for example, it can be 0.1°C, 0.12°C, 0.13°C, 0.15°C, 0.18°C, 0.2°C, 0.22°C, 0.23°C, 0.25°C, 0.3°C, 0.32°C, 0.35°C, 0.4°C, 0.45°C, 0.48°C or 0.5°C, etc., but not limited to the listed values, other values not listed in this range are also applicable.

[0039] Preferably, the fluctuation range of the terminal temperature is 0.1-2 slpm fluctuation up and down on the terminal flow rate, for example, it can be 0.1 slpm, 0.12 slpm, 0.13 slpm, 0.14 slpm, 0.15 slpm, 0.16 slpm, 0.18 slpm, 0.19 slpm, 0.2 slpm, 0.5 slpm, 1 slpm, 1.2 slpm, 1.5 slpm, 1.8 slpm, 1.9 slpm or 2.0 slpm, etc.

[0040] Preferably, the certain time is 8-12 min, for example, it can be 8 min, 8.5 min, 8.9 min, 9.4 min, 9.8 min, 10.3 min, 10.7 min, 11.2 min, 11.6 min or 12 min, etc., but not limited to the listed values, other values not listed in this range are also applicable.

[0041] Preferably, the protective gas comprises argon.

[0042] Preferably, the fusion is performed by a Czochralski single crystal furnace platform.

[0043] Compared with the prior art, the present application has at least the following beneficial effects:

[0044] For the fusion process of low pot rotation and low furnace pressure single crystal rod drawing, the fusion method of low-oxygen single crystal silicon seed provided by the present application can significantly improve the crystal formation rate by 3%-5% by controlling the argon flow rate during the fusion process to be greater than the conventional flow rate and gradually reducing the argon flow rate as the temperature of the molten silicon surface decreases. DETAILED DESCRIPTION

[0045] For the purpose of understanding the present application, the present application is illustrated with the following examples. It will be apparent to a person skilled in the art that the examples are only for the purpose of understanding the present application and should not be considered as a specific limitation to the present application.

[0046] It should be understood that the terms "first", "second" and the like, are used to describe various elements, but do not imply or imply relative importance or a specific number of the indicated technical features. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0047] The complete crystal pulling process of low-oxygen single crystal silicon is provided in the following examples and comparative examples of the present application, which is carried out by using a Czochralski furnace table, and the specific steps include:

[0048] Melt process: the pot is rotated at 3 rpm, the furnace pressure is 11 torr, the temperature is increased from room temperature to about 1445℃, and the argon flow rate is 150 slmp.

[0049] Temperature adjustment process: the pot is rotated at 5 rpm, the furnace pressure is 11 torr, the temperature is 1445℃ to 1452℃, and the argon flow rate is 150 slmp.

[0050] Fusion process: according to the scheme of the following examples and comparative examples.

[0051] Crystal pulling process: the pot is rotated at 5 rpm, the furnace pressure is 10 torr, the temperature is 1448.5℃ to 1450.5℃, and the argon flow rate is 100 slmp.

[0052] Shoulder process: the pot is rotated at 5 rpm, the furnace pressure is 7 torr, the temperature is 1448.5℃ to 1450.5℃, and the argon flow rate is 100 slmp.

[0053] Shoulder process: the pot is rotated at 5 rpm, the furnace pressure is 7 torr, the temperature is 1448.5℃ to 1450.5℃, and the argon flow rate is 100 slmp.

[0054] The parameters of the equal-diameter early stage process, the equal-diameter middle stage process, the equal-diameter late stage process and the finishing process are shown in the following table:

[0055] Table 1

[0056]

[0057] Example 1

[0058] The embodiment provides a low-oxygen monocrystalline silicon seed crystal welding method, and the welding method comprises the following steps:

[0059] During the whole welding process, the furnace pressure is 6 torr, the crucible rotation is 5 rpm, the argon flow rate is maintained at the argon flow rate in the temperature adjustment process (150 slpm) at the beginning of the welding, the temperature of the molten silicon liquid surface is heated to the first temperature 1453 DEG C, the argon flow rate is adjusted to the first flow rate 200 slpm, the temperature is continuously increased to 1460 DEG C, and the first flow rate (allowing a fluctuation of ± 0.5 DEG C) is maintained until the seed crystal is welded;

[0060] When the temperature of the molten silicon liquid surface is reduced to the A temperature 1458 DEG C, the flow rate of the protective gas is reduced to the A1 flow rate 175 slpm; when the temperature of the molten silicon liquid surface is reduced to the B temperature 1455 DEG C, the flow rate of the protective gas is reduced to the B1 flow rate 151 slpm; that is, during the process of reducing the temperature of the molten silicon liquid surface and reducing the flow rate of the protective gas, the relationship between the flow rate Q of the protective gas and the temperature T of the molten silicon liquid surface is Q = 8.330T-11970, wherein the unit of T is DEG C, and the unit of Q is slpm.

[0061] The temperature of the molten silicon liquid surface is continuously reduced until the temperature of the molten silicon liquid surface is the terminal temperature 1452 DEG C, the flow rate of the argon is adjusted to the terminal flow rate 125 slpm, and the temperature is allowed to fluctuate up and down by 0.2 DEG C and the flow rate is allowed to fluctuate up and down by 0.2 slpm for 10 min;

[0062] The flow rate of the argon is restored to the normal flow rate (adjusted to the argon flow rate in the crystal pulling process 100 slpm), and the welding process is completed.

[0063] Embodiment 2

[0064] The embodiment provides a low-oxygen monocrystalline silicon seed crystal welding method, and the welding method comprises the following steps:

[0065] During the whole welding process, the furnace pressure is 5 torr, the crucible rotation is 5 rpm, the argon flow rate is maintained at the argon flow rate in the temperature adjustment process (150 slpm) at the beginning of the welding, the temperature of the molten silicon liquid surface is heated to the first temperature 1455 DEG C, the argon flow rate is adjusted to the first flow rate 210 slpm, the temperature is continuously increased to 1461 DEG C, and the first flow rate (allowing a fluctuation of ± 0.5 DEG C) is maintained until the seed crystal is welded;

[0066] The temperature of the molten silicon surface is first reduced to A temperature 1459°C, and the flow rate of the protective gas is reduced to Al flow rate 182 slpm; the temperature of the molten silicon surface is secondly reduced to B temperature 1456°C, and the flow rate of the protective gas is reduced to Bl flow rate 155 slpm; that is, in the process of reducing the temperature of the molten silicon surface and reducing the flow rate of the protective gas, the relationship between the flow rate Q of the protective gas and the temperature T of the molten silicon surface is Q=8.331T-11973, wherein the unit of T is °C, and the unit of Q is slpm.

[0067] The temperature of the molten silicon surface is continuously reduced until the temperature of the molten silicon surface is final temperature 1451°C, the flow rate of argon is adjusted to final flow rate 114 slpm, and is maintained for 12 min with an allowable fluctuation of 0.1°C in temperature and 0.3 slpm in flow rate;

[0068] The flow rate of argon is restored to the normal flow rate (adjusted to be 100 slpm of the argon flow rate in the crystal pulling process), and the fusing process is completed.

[0069] Example 3

[0070] The present embodiment provides a fusing method of low-oxygen single crystal silicon seeds, which comprises the following steps:

[0071] The furnace pressure is 6 torr and the crucible rotation is 6 rpm in the whole fusing process. When the fusing starts, the flow rate of argon is the normal flow rate (maintained at 150 slpm of the argon flow rate in the temperature adjustment process), heating is performed until the temperature of the molten silicon surface is first temperature 1450°C, the flow rate of argon is adjusted to first flow rate 195 slpm, the temperature is continuously increased to 1458°C and maintained at the first flow rate (allowable fluctuation of ±0.4°C) until the seed is completed fusing;

[0072] The temperature of the molten silicon surface is first reduced to A temperature 1458°C, and the flow rate of the protective gas is reduced to Al flow rate 172 slpm; the temperature of the molten silicon surface is secondly reduced to B temperature 1456°C, and the flow rate of the protective gas is reduced to Bl flow rate 155 slpm; that is, in the process of reducing the temperature of the molten silicon surface and reducing the flow rate of the protective gas, the relationship between the flow rate Q of the protective gas and the temperature T of the molten silicon surface is Q=8.33T-11973, wherein the unit of T is °C, and the unit of Q is slpm.

[0073] The temperature of the molten silicon surface is continuously reduced until the temperature of the molten silicon surface is final temperature 1452°C, the flow rate of argon is adjusted to final flow rate 122 slpm, and is maintained for 8 min with an allowable fluctuation of 0.1°C in temperature and 0.3 slpm in flow rate;

[0074] The flow rate of argon is restored to the normal flow rate (adjusted to be 100 slpm of the argon flow rate in the crystal pulling process), and the fusing process is completed.

[0075] Example 4

[0076] This example provides a low-oxygen monocrystalline silicon seed fusing method, which is the same as example 1 except that the flow rate of argon is adjusted to a first flow rate of 100 slpm, which will not be repeated here.

[0077] Example 5

[0078] This example provides a low-oxygen monocrystalline silicon seed fusing method, which is the same as example 1 except that the flow rate of argon is adjusted to a first flow rate of 230 slpm, which will not be repeated here.

[0079] Example 6

[0080] This example provides a low-oxygen monocrystalline silicon seed fusing method, which is the same as example 1 except that when the temperature of the molten silicon liquid surface is first reduced to an A temperature of 1458°C, the flow rate of the protective gas is reduced to an A1 flow rate of 145 slpm, which will not be repeated here.

[0081] Example 7

[0082] This example provides a low-oxygen monocrystalline silicon seed fusing method, which is the same as example 1 except that when the temperature of the molten silicon liquid surface is first reduced to an A temperature of 1458°C, the flow rate of the protective gas is reduced to an A1 flow rate of 190 slpm, which will not be repeated here.

[0083] Example 8

[0084] This example provides a low-oxygen monocrystalline silicon seed fusing method, which is the same as example 1 except that when the temperature of the molten silicon liquid surface is secondly reduced to a B temperature of 1455°C, the flow rate of the protective gas is reduced to a B1 flow rate of 120 slpm, which will not be repeated here.

[0085] Example 9

[0086] This example provides a low-oxygen monocrystalline silicon seed fusing method, which is the same as example 1 except that when the temperature of the molten silicon liquid surface is secondly reduced to a B temperature of 1455°C, the flow rate of the protective gas is reduced to a B1 flow rate of 165 slpm, which will not be repeated here.

[0087] Comparative Example 1

[0088] This comparative example provides a conventional fusing method, i.e., after entering the fusing stage, the flow rate of argon is maintained at 100 slpm unchanged until the end of fusing.

[0089] Test method: The oxygen content at the transition shoulder of the final obtained single crystal silicon rod is tested by an infrared spectrometer, and the crystal formation rate of the single crystal silicon rod is evaluated by the ratio of the weight of the single crystal formed in a single furnace to the amount of the raw material.

[0090] The test results of the above examples and comparative examples are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] From Table 1, it can be seen that:

[0095] For the fusion process of low pot rotation and low furnace pressure single crystal rod drawing, the fusion method of the low-oxygen single crystal silicon seed provided by the present application can significantly improve the crystal formation rate by 3%-7% by controlling the argon flow rate in the fusion process to be greater than the conventional flow rate and gradually reducing the argon flow rate as the temperature of the molten silicon surface decreases.

[0096] In Example 3, the argon flow rate is too small, the liquid surface shakes severely, resulting in a low shoulder forming survival rate, thereby causing the crystal formation rate to decrease compared with Example 1. In Example 4, the argon flow rate is too large, the protective gas consumption is high, the cost is high, and the crystal formation rate decreases compared with Example 1.

[0097] In Example 6, the argon flow rate decreases too quickly, the liquid surface temperature changes dramatically, resulting in uneven melt temperature, and the surface temperature (test temperature) of the melt deviates greatly from the actual temperature of the whole melt, thereby causing a low shoulder forming survival rate and a decrease in the crystal formation rate compared with Example 1. In Example 7, the argon flow rate decreases too slowly, the protective gas consumption is high, the cost is high, and the crystal formation rate decreases compared with Example 1. Similar conclusions can be drawn from Examples 8-9.

[0098] The above examples illustrate the detailed features of the present application, but the present application is not limited to the above detailed features, i.e. it does not mean that the present application must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvement of the present application, equivalent replacement of the technical features selected by the present application, addition of auxiliary technical features, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for fusing low-oxygen single-crystal silicon seeds, characterized in that, The welding method includes: At the start of the fusion process, the flow rate of the protective gas is at the normal flow rate. When the temperature of the molten silicon surface reaches the first temperature, the flow rate of the protective gas is adjusted to the first flow rate. The temperature is continuously increased and the first flow rate is maintained until the seed crystal is fused. Lower the temperature of the molten silicon surface and reduce the flow rate of the protective gas; When the temperature of the molten silicon surface reaches the final temperature, the flow rate of the protective gas is adjusted to the final flow rate; the first temperature is greater than the final temperature, the first flow rate is greater than the final flow rate, and the first flow rate is greater than the normal flow rate. For a fixed period of time, the final flow rate is kept constant. After the time is up, the flow rate of the protective gas is restored to the normal flow rate, and the welding process is completed.

2. The welding method according to claim 1, characterized in that, The final temperature of the continuous heating is 1458–1461°C.

3. The welding method according to claim 1, characterized in that, The first temperature is 1450–1455°C; And / or, the first flow rate is 25 to 110 slpm higher than the normal flow rate, and the first flow rate is 110 to 210 slpm.

4. The welding method according to any one of claims 1 to 3, characterized in that, The reduction of the temperature of the molten silicon surface and the reduction of the protective gas flow rate include: When lowering the temperature of the molten silicon surface to temperature A, gradually reduce the flow rate of the protective gas to the flow rate A1. Secondly, when lowering the temperature of the molten silicon surface to temperature B, gradually reduce the flow rate of the protective gas to the flow rate of B1; Wherein, temperature A is higher than temperature B; and flow rate A1 is greater than flow rate B1.

5. The welding method according to claim 4, characterized in that, The temperature range of A is 1455–1459°C, and the flow rate range of A1 is 150–183 slpm; The temperature range of B is 1450–1456°C, and the flow rate of B1 ranges from 105 to 160 slpm.

6. The welding method according to claim 4, characterized in that, The temperature difference between temperature A and temperature B is 3 to 5°C. The difference between the A1 flow rate and the B1 flow rate is 25–35 slpm.

7. The welding method according to claim 4, characterized in that, The A1 flow rate is lower than the first flow rate; And / or, the difference between the A1 flow rate and the first flow rate is 15 to 25 slpm.

8. The welding method according to any one of claims 1 to 3, characterized in that, The final temperature is 1451–1452°C; The terminal flow rate is 120–140 slpm.

9. The welding method according to any one of claims 1 to 3, characterized in that, The method further includes maintaining the flow rate within the range of fluctuation and the temperature within the range of fluctuation for a specific time. The fluctuation range of the terminal flow rate is 0.1 to 0.5°C above and below the terminal temperature; The fluctuation range of the final temperature is 0.1 to 2 slpm above and below the final flow rate; The specific time is 8 to 12 minutes.

10. The welding method according to any one of claims 1 to 3, characterized in that, The protective gas includes argon; And / or, the welding is performed using a single-crystal furnace.

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